The present invention relates to a packaging corrugated cardboard which is both lightweight and excellent in heat insulation. Specifically, this invention concerns a heat-insulating corrugated cardboard of great water-resistant strength, characterized in that its corrugated core is formed of a foamed plastic sheet which may be laminated on one side or both sides with a plastic film or films, and a method for making such a cardboard. More specifically, this invention is directed to a heat-insulating corrugated cardboard designed to be used as the packaging material which is required to protect petals or perishables against heat while keeping them fresh and/or to have resistance to scratching and scuffing and shock absorption, and a method for making it.